Process for preparing 2-hydroxybenzoic aldehydes

Abstract

There is disclosed a catalytic process for preparing, from phenols and formaldehyde 2-hydroxybenzoic aldehydes some of which are new in the art and, more particularly, a high-selectivity process for preparing the aldehydes by direct synthesis from phenols having at least a free ortho position and formaldehyde, in the presence of a catalyst consisting of anhydrous stannous and/or stannic chloride and of an aprotic binder.

What we claim is: 
     
       1. Process for preparing 2-hydroxy-benzoic aldehydes having the general formula (I): ##STR3## wherein R, R 1 , R 2  and R 3 , which can be the same or different, represent hydrogen atoms; alkyl, aryl, cycloalkyl, alkoxyl, hydroxyl, or acylamino groups, or halogen; characterized in that a phenol of general formula (II) ##STR4## wherein R, R 1 , R 2  and R 3  have the same meaning as in general formula (I), is condensed with formaldehyde at temperatures of from about 90° to 150° C., in a substantially stoichiometric molar ratio between phenol (II) and formaldehyde, in the presence of anhydrous stannous and/or stannic chloride, in ratios comprised between about 0.02 and 0.2 mole expressed as Sn for one mole of phenol (II), and of a binder selected from the group consisting of pyridine, alkylpyridines, acetylpyridines, hexamethylphosphotriamide, tetramethylethylenediamine, tetramethylpropylenediamine, quinolines, quinoxalines, anilines, substituted anilines and tertiary amines, in an aprotic solvent. 
     
     
       2. The process of claim 1, in which the condensation reaction is carried out at a temperature of about 110° C. 
     
     
       3. The process of claim 1, in which the phenol of general formula (II) is condensed with paraformaldehyde. 
     
     
       4. The process of claim 1, in which about 0.1 mole of catalyst, expressed as Sn, is used per mole of the phenol (II). 
     
     
       5. The process of claim 1, in which the binder is used in a molar ratio of from about 0.1 to 0.6 mole, per mole of the phenol (II). 
     
     
       6. The process of claim 5, in which the binder is used in an amount of about 0.4 mole per mole of the phenol (II). 
     
     
       7. The process of claim 1, in which the aprotic solvent is at least one compound selected from the group consisting of toluene, xylenes, cumene, alkylbenzenes, decalin and anisole. 
     
     
       8. The process of claim 1, in which the catalyst is anhydrous SnCl 2 .